Behave WG                                                    J. Korhonen
Internet-Draft                                    Nokia Siemens Networks
Intended status: Standards Track                      T. Savolainen, Ed.
Expires: January 2, 2011                                           Nokia
                                                            July 1, 2010


        EDNS0 Flags Indicating AAAA Record Synthesis and Format
               draft-korhonen-edns0-synthesis-flag-00.txt

Abstract

   Advanced hosts and applications benefit of the knowledge of an IPv6
   address, AAAA record, and a possible synthesis taking place in the
   network.  This specification defines ENDS0 flag bits for
   communicating whether the synthesis is taking place, what is the used
   IPv6 address format, and the IPv6 prefix and suffix used by the
   DNS64.  The communicated information enables hosts to perform a local
   IPv6 address synthesis and to extract the IPv4 address out of the
   synthesized IPv6 address.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 2, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements and Terminology  . . . . . . . . . . . . . . . . . 3
   3.  EDNS0 flags for indicating address synthesis  . . . . . . . . . 3
   4.  Host behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6





























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1.  Introduction

   As the networks transition to IPv6, connectivity to IPv4-only domains
   has to be provided.  NAT64 [I-D.ietf-behave-v6v4-xlate-stateful] and
   DNS64 [I-D.ietf-behave-dns64] technologies can be utilized to make
   IPv4-only peers look like being reachable over IPv6.  The DNS64
   utilizes IPv6 address synthesis to create local IPv6 presentations of
   peers having only IPv4 addresses.  Applications utilizing DNS for
   resolving peers' IPv6 addresses can work seamlessly through protocol
   translation taking place at NAT64.

   The DNS64 cannot serve applications that are not using DNS, such as
   those receiving and using IPv4 address referrals.  Such applications
   could nevertheless be able to work through NAT64, provided they are
   able to create locally valid IPv6 presentations of peers' IPv4
   addresses.

   This specification describes a method for advanced applications to
   learn the information required for a local IPv6 address synthesis.

   The knowledge of IPv6 address synthesizing taking place may also be
   useful if DNS64 is present in a dual-stack network access.  In such
   cases hosts may choose to use IPv4 addresses instead of synthesized
   IPv6 addresses, and hence avoid traversal through NAT64.


2.  Requirements and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


3.  EDNS0 flags for indicating address synthesis

   The mechanism for informing AAAA record synthesis taking place and
   the used addressing format is using three bits of the ENDS0 OPT
   header in the DNS response.  The bits are structured as follows:













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                   +0 (MSB)                +1 (LSB)
            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
         0: |   EXTENDED-RCODE      |       VERSION         |
            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
         2: |DO|   SY   |           Z                       |
            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    Possible values for SY-bits are:

             000 reserved
             001 prefix length /32
             010 prefix length /40
             011 prefix length /48
             100 prefix length /56
             101 prefix length /64
             110 prefix length /96
             111 address is not synthesized

                                 Figure 1

   The prefix length corresponds to the address formats documented in
   "IPv6 Addressing of IPv4/IPv6 Translators document"
   [I-D.ietf-behave-address-format] section 2.2.

   The absence of the EDNS0 option means that either no synthesis took
   place or the DNS64 does not support this specification.  Either way,
   when the EDNS0 option is missing, the host cannot conclude for
   certain whether the AAAA response was synthesized or not.  However,
   if the host knows the name it asked for cannot have a real AAAA
   record, it MAY search for the IPv4 address inside the received IPv6
   address, and if found then make an educated guess of the address
   format used by the DNS64.  The host MAY learn the IPv4 address via an
   A query, or have the address preconfigured.

   [Editor's note: currently using extended flags has the least on-wire
   overhead.  However, it also allocates multiple scarce flag bits.
   Therefore, the use of extended OPTION-CODE could be an alternative
   approach.]


4.  Host behavior

   A host requiring information for a local IPv6 address synthesis or
   NAT64 avoidance SHALL send a DNS query for an AAAA record of a well-
   known IPv4-only fully qualified domain name (e.g. ip4.example.com)
   [editor's note: whether this domain name must be reserved by IANA is
   to be decided].  This may happen, for example, at the moment the host
   is configured an IPv6 address of a DNS server.  This may also happen



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   at the time first DNS query for AAAA record is initiated.

   If a host receives a negative reply, it learns there is no NAT64 in
   the network.  If the host receives AAAA reply, it knows the network
   is utilizing IPv6 address synthesis.  If the received IPv6 address
   has a well-known prefix, the host can use that information for a
   local IPv6 address synthesis.  If the prefix is not well-known, the
   host reads the ENDS0 flag values to learn the used address format.
   Using the learned prefix length information, the host extracts from
   the received IPv6 address the information used by the network for
   IPv6 address synthesis (prefix, suffix, u-bit).

   The information required for a local IPv6 address synthesis SHOULD be
   made available for applications to utilize.


5.  Security Considerations

   No security considerations have been identified.


6.  IANA Considerations

   EDNS0 RFC 2671 [RFC2671] defines 16 bit extended flag field in the
   OPT RR.  These bits are encoded into the TTL field of the OPT record
   (see Section 4.6 of RFC 2671).

   This specification reserves three of extended flag bits as the SY-
   bits.  It is requested that the next available consequent leftmost
   bits are allocated.


7.  Acknowledgements

   The authors would like to acknowledge Andrew Sullivan for presenting
   general idea of ENDS0 option and SY-bit in Behave WG mailing list.


8.  Normative References

   [I-D.ietf-behave-address-format]
              Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators",
              draft-ietf-behave-address-format-08 (work in progress),
              May 2010.

   [I-D.ietf-behave-dns64]
              Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,



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              "DNS64: DNS extensions for Network Address Translation
              from IPv6 Clients to IPv4 Servers",
              draft-ietf-behave-dns64-09 (work in progress), March 2010.

   [I-D.ietf-behave-v6v4-xlate-stateful]
              Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers",
              draft-ietf-behave-v6v4-xlate-stateful-11 (work in
              progress), March 2010.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2671]  Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
              RFC 2671, August 1999.


Authors' Addresses

   Jouni Korhonen
   Nokia Siemens Networks
   Linnoitustie 6
   FI-02600 Espoo
   Finland

   Email: jouni.nospam@gmail.com


   Teemu Savolainen (editor)
   Nokia
   Hermiankatu 12 D
   FI-33720 Tampere
   Finland

   Email: teemu.savolainen@nokia.com















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